Slice 7: expose git commands as MCP tools

Add git_fetch/git_pull/git_push/git_commit/git_discard_changes MCP tools as thin adapters over the service (actor=claude), completing 1.7 symmetry so Claude can run the same commands as the right-click menu. git_discard_changes is flagged destructive (confirm first, 1.4). Extended the MCP test with a git_commit round-trip; synced AGENT.md 8.1 tool list.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/mcp/mcp_test.go

@@ -201,6 +201,21 @@ func TestMCPRoundTrip(t *testing.T) {
 	if !res.IsError {
 		t.Fatalf("expected IsError acking with no pending switch")
 	}
+
+	// --- git_commit via MCP (adapter wiring) --------------------------------
+	if err := os.WriteFile(filepath.Join(repoPath, "extra.txt"), []byte("x\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	res, err = cs.CallTool(ctx, &mcpsdk.CallToolParams{
+		Name:      "git_commit",
+		Arguments: map[string]any{"path": repoPath, "message": "add extra via mcp"},
+	})
+	if err != nil {
+		t.Fatalf("git_commit: %v", err)
+	}
+	if res.IsError {
+		t.Fatalf("git_commit tool error: %+v", res.Content)
+	}
 }
 
 // decodeResult unmarshals the JSON text content of a tool result into v.